High-pass T-networks with integral transformer for gaseous discharge lamps

ABSTRACT

For coupling one, or more, gaseous discharge lamps to a high-frequency AC power-source a ballasting (current-limiting) network employs a first capacitor, a second capacitor, and a transformer having a primary winding coupled to the high-frequency AC power-source by the first capacitor and a secondary winding coupled to the gaseous discharge lamp by the second capacitor.

This is a divisional of copending application Ser. No. 07/443,588 filedon Nov. 29, 1989.

TECHNICAL FIELD

The present invention relates to ballasts for gaseous-discharge lampsgenerally and more particularly to a safe ballasting network.

BACKGROUND ART

A ballast (at least as the term is used herein) is something which isemployed to limit the level of a current through a gaseous-dischargelamp. For example, an inductor functions as a ballast when the inductoris connected in series with a fluorescent lamp across a 120 volt, 60 Hz,AC power line. Although satisfactory for many applications, thiscombination is less than ideal. For one thing, such a combinationpresents a less than ideal power factor to the AC power line. Inaddition, at 60 Hz, inductors (of any reasonable size) dissipate arelatively large amount of power generating a relatively large amount ofheat. Further, fluorescent lamps operate more efficiently when drivenfrom a high-frequency source of AC power, such as, for example, the ACpower source which is disclosed in the Ronald A. Lesea U.S. Pat. No.4,415,839, entitled "Electronic Ballast For Gaseous Discharge Lamps."

Portions of the above-mentioned ballast are illustrated (herein) in FIG.1 of the drawing generally designated by the number 10. Illustrated withballast 10 is a (load that employs at least one) gaseous discharge lamp,which is designated 12. Ballast 10 is shown to employ apower-factor-correcting network 20; a DC power supply 22; a pair ofswitches (transistors), which are respectively designated 24 and 26; acurrent-limiting network 28; and a pulse generator 30. DC power supply22 is of a voltage-doubler type which develops two DC potentials withrespect to a "reference" potential level that is developed on a line 42.DC power supply 22 develops on a "DC power-supply line" 44 a (twicepeak) potential level and on a lamp "return" line 46 a potential levelone half the line 44 potential level. To improve the power factor DCpower supply 22 presents to an AC power line (by restricting the amountof power the DC power supply can obtain from the AC power line duringpeaks of the line cycle), the DC power supply is connected in serieswith power-factor-correcting network 20 across a 120 volt, 60 Hz, ACpower line, which is represented by a "neutral" line 48 and a "hot" line50. Switches (transistors) 24 and 26 are connected in a totem-poleconfiguration in which the channels of the transistors are connected inseries between DC power-supply line 44 and reference line 42. In otherwords, the channel of switch (transistor) 24 is configured with one endof the channel connected to line 44 and with the other end of thechannel connected to a ("high-frequency AC power-source") line 56., and,the channel of switch (transistor) 26 is configured with one end of thechannel connected to line 56 and with the other end of the channelcoupled (by a resistor, not shown) to line 42. The gates of switches(transistors) 24 and 26 are each coupled by a respective one of twolines, designated 62 and 64, to pulse generator 30. (In one embodiment)pulse generator 30 is configured to drive the switches (transistors), inturn, so as to develop on line 56, a source of high-frequency AC power,the waveform of which approximates a square wave. Lamp (load) 12 iscoupled by current-limiting network 28 between high-frequency ACpower-source line 56 and return line 46. Specifically, current-limitingnetwork 28 is connected between line 56 and a line 68; and, lamp (load)12 is connected between lines 68 and 46. As will become apparentshortly, in some embodiments, current-limiting network 28 is alsoconnected to return line 46.)

For purposes of discussion, for a moment, assume that lamp 12 includesbut a single fluorescent lamp of the (four-foot long) type which iscommonly designated F40T12 (fluorescent, 40-watt, tubular,twelve-eights-inch diameter). Normally an F40T12 lamp requires apotential level (voltage drop) of approximately 200 volts for ignitionand operates with a current level of approximately 0.4 amperes (at 60Hz), developing a voltage drop of approximately 100 volts. Also, for amoment, assume, to ignite the lamp, that ballast 10 develops on line 56a source of high-frequency AC power having a peak potential level(which, for a square wave, is the same as the RMS potential level) of200 volts (somewhat more than the 140 volts actually developed). Tolimit the level of the current through lamp 12, first, assume, thatcurrent-limiting network 28 of ballast 12 (shown in FIG. 1) includes buta simple series resistor 200, as is illustrated in (prior art) FIG. 2A.Assume, to limit the level of the current through lamp 12 to 0.4amperes, that resistor 200 has a resistance of 250 ohms, dropping 100volts of the 200 volts developed on high-frequency AC power-source line56. Then, as a consequence, resistor 200 would dissipate, as heat, 40watts of power. Further, as a consequence, ballast 10 (shown in FIG. 1)would be required to provide 80 watts of power. Obviously, such aballast (network) would not be very efficient.

Next, to limit the level of the current through lamp 12, assume thatcurrent-limiting network 28 of ballast 10 (shown in FIG. 1) includes buta simple series inductor 220, as is illustrated in (prior art) FIG. 2B.Assume, to limit the level of the current through lamp 12 to 0.4 amperesthat inductor 220 has a reactance of 380 ohms (at the square-wavefundamental frequency). (Since the voltages are in phase quadrature, thelevel of the voltage drop developed across inductor 220 is equal to thesquare root of 182 volts (the Fourier-adjusted level of the voltage (200volts assumed) developed on high-frequency AC power-source line 56)squared minus 100 volts (the level of the voltage drop developed acrosslamp 12) squared, which equals approximately 152 volts. The reactance ofinductor 220 is equal to 152 volts (the level of the voltage dropdeveloped across the inductor) divided by 0.4 amperes (the level of thecurrent), which equals approximately 380 ohms.) In this case, ballast 10would be required to provide 80 VA into a load which is highlyinductive. (Of course, inductor 220 stores, rather than dissipating asheat, in this case, approximately, 61 VA (152 volts times 0.4 amperes.)Another disadvantage of using but a simple series inductor (220) forcurrent-limiting network 28 is that the inductor must be relativelylarge in order to handle the 61 VA. Yet another disadvantage is that theswitches (transistors) must have the "generating capacity" to "generate"the total VA. The relatively high current level (0.4 amperes) throughthe effective (drain-to-source) "on resistance" of the switches(transistors) 24 and 26 results in a relative high power dissipationlevel in the transistors. As a consequence, ballast 10 would not only berelatively inefficient, but would require relatively efficient (largeand expensive) heat sinks. (The effective transistor on resistance maybe reduced by using (larger and) more expensive transistors.) (In the C.Stevens U.S. Pat. No. 4,684,850, a current-limiting network (ballast)including but a simple series inductor is shown, in FIGS. 4 and 5,designated 53. A current-limiting network (ballast) including but simpleseries capacitors (one for each of several lamps) is shown in the D. BayU.S. Pat. No. 4,613,796, designated 57.)

Illustrated in (prior art) FIG. 2C, is a current-limiting network thatincludes an inductor 240 connected between high-frequency ACpower-source line 56 and line 68 and a capacitor 242 connected betweenline 68 and return line 46. Such a current-limiting network, which isreferred to herein as a "low-pass" "L-C" or "L-section" network, isuseful in that it may be used to provide an impedance transformation,providing a relatively high impedance to lamp 12 while providing arelatively low impedance at, or near, a zero degree phase angle, toswitches (transistors) 24 and 26, reducing the level of the currentthrough the transistors. (Such a "low-pass" "L-C" or "L-section"current-limiting network (ballast) is shown, designated 65 and 63 inFIG. 3, of the Z Zansky U.S. Pat. No. 4,370,600 and, designated, "L" and"C" in FIG. 1 of the J. Walden U.S. Pat. No. 4,346,332. Further, such anetwork is used in conjunction with a step-up auto-transformer in the W.Knoll et al. U.S. Pat. Nos. 4,532,456 and 4,525,649. The '456 networkdrives a single lamp; and, the '649 network drives multiple lamps.)Further, such a current-limiting network is useful in that it may beused to provide a "resonant rise" for starting lamp 12. (For example, ifinductor 240 had a reactance of j200 ohms and if capacitor 242 had areactance of -j300 ohms (both at the square-wave fundamental frequency),the delta (difference) would be 100 ohms and there would be a net threetimes voltage rise across capacitor 242.) (Protection for the componentsof an L-section current-limiting network (ballast) at resonance is thesubject of a number of the series of O. Nilssen U.S. Pat. Nos.,including U.S. Pat. No. 4,461,980.)

Finally, illustrated in (prior art) FIG. 2D, is a current-limitingnetwork that includes an inductor 260 connected between high-frequencyAC power-source line 56 and a node 262, a capacitor 264 connectedbetween node 262 and return line 46, and another inductor 266 connectedbetween node 262 and line 68. Such a current-limiting network, which isreferred to herein as a "low-pass" "L-C-L" or "T-section" network, isuseful in that it provides an extra degree of "design freedom" notprovided by the current-limiting network shown in FIG. 2C. (Such a"low-pass" "L-C-L" or "T-section" current-limiting network (ballast) isshown in the L. Filgas, Jr. et al U.S. Pat. No. 4,358.712; K. HashimotoU.S. Pat. No. 4,544,863; C. Stevens U.S. Pat. No. 4,277,728; and R.Munson U.S. Pat. No. 4,641,061. The components (L, C, and L,respectively) of the current-limiting networks are designated 10, 12,and 18 in FIG. 1 of the L. Filgas, Jr. et al patent; "L," "C2," and "CI"in FIG. 4 of the K. Hashimoto patent; 47, 46, and 45 in FIG. 4A of theC. Stevens patent; and LI, CI, and C4 (L2, C2, and C5 or L3, C3, and C6)in the R. Munson patent.

It is important to note that the networks illustrated in FIGS. 2B-Dprovide attenuation of the level of the harmonics of the square-wavefrequency. As a consequence, the waveform of the "high-frequency ACpower" actually driving lamp(s) 12 is much closer to a sinusoidal waverather than a square wave.

The above mentioned ballasts are disadvantageous in that they providelittle isolation from the AC power line. As a consequence, the abovementioned ballasts may pose a safety hazard (danger of electrocution) toall who come in contact there with.

DISCLOSURE OF THE INVENTION

It is therefore the primary object of the present invention to provide agaseous-discharge-lighting system which is safe.

Another object of the present invention is to provide agaseous-discharge-lighting system which is relatively efficient.

Still another object of the present invention is to provide a agaseous-discharge-lighting system which is relatively inexpensive.

Yet another object of the present invention is to provide a networkwhich presents a relatively high power factor to a high-frequency ACpower source.

A further object of the present invention is to provide a safeballasting network which is relatively efficient and relativelyinexpensive.

Briefly, for coupling one, or more, gaseous discharge lamps to ahigh-frequency AC power-source the presently preferred embodiment of aballasting network in accordance with the present invention employs afirst capacitor, a second capacitor, and a transformer having a primarywinding coupled to the high-frequency AC power-source by the firstcapacitor and a secondary winding coupled to the gaseous discharge lampby the second capacitor.

These and other objects of the present invention will no doubt becomeapparent to those skilled in the art after having read the detaileddescription of the presently preferred embodiment of the presentinvention which is illustrated in the figures of the drawing.

BRIEF DESCRIPTION OF THE FIGURES IN THE DRAWING

FIG. 1 is a schematic diagram of a portion of the "Electronic BallastFor Gaseous Discharge Lamps" disclosed in the above-mentioned Ronald A.Lesea U.S. Pat. No. 4,415,839.

FIG. 2A (prior art) is a schematic diagram of a simple resistor for usein one embodiment of the ballasting network shown in FIG. 1.

FIG. 2B (prior art) is a schematic diagram of a simple inductor for usein another embodiment of the ballasting network shown in FIG. 1.

FIG. 2C (prior art) is a schematic diagram of a low-pass L-C (L-section)network for use in still another embodiment of the ballasting networkshown in FIG. 1.

FIG. 2D (prior art) is a schematic diagram of a low-pass L-C-L(T-section) network for use in yet another embodiment of the ballastingnetwork shown in FIG. 1.

FIG. 3 is a schematic diagram of a gaseous-discharge-lighting system inaccordance with the present invention.

FIG. 4 is a schematic diagram of the presently preferred embodiment of agaseous-discharge-lighting system in accordance with the presentinvention.

FIG. 5 is a schematic diagram of a high lamp impedance variation of thethe gaseous-discharge-lighting system shown in FIG. 4.

FIGS. 6A-D are schematic diagrams of Q-enhanced variations of the thecurrent-limiting network shown in FIG. 4.

FIG. 7 is a schematic diagram of a gaseous-discharge-lighting system inaccordance with the present invention configured to drive the parallelcombination of multiple gaseous discharge lamps.

FIG. 8 is a schematic diagram of a gaseous-discharge-lighting system inaccordance with the present invention configured to drive the"quasi-parallel" combination of multiple gaseous discharge lamps.

FIG. 9 is a schematic diagram of a combination of thegaseous-discharge-lighting systems shown in FIGS. 7 and 8.

FIG. 1OA is a block diagram of a current-limiting network in accordancewith the present invention driven by a high-frequency AC power sourcewhich appears to the network as a voltage source.

FIG. 1OB is a block diagram of a current-limiting network in accordancewith the present invention driven by a high-frequency AC power sourcewhich appears to the network as a current source.

BEST MODE FOR CARRYING OUT THE INVENTION

Illustrated in FIG. 3 of the drawing generally designated by the number300 is one embodiment of a gaseous-discharge-lighting system inaccordance with the present invention. Preferably, except as notedbelow, gaseous-discharge-lighting system 300 uses a portion of the"Electronic Ballast For Gaseous Discharge Lamps" which is disclosed inthe above-mentioned Ronald A. Lesea U.S. Pat. No. 4,415,839 and which isillustrated in FIG. 3 generally designated 310. In addition,gaseous-discharge-lighting system 300 uses a (load that employs at leastone) gaseous discharge lamp, which is designated 312. Ballast 310 isshown to employ a power-factor-correcting network 320; a DC power supply322; a pair of switches (transistors), which are respectively designated324 and 326; a current-limiting network 328., and a pulse generator 330.DC power supply 322 is, preferably, of a voltage-doubler type whichdevelops two DC potentials with respect to a "reference" potential levelthat is developed on a line 342. DC power supply 322 develops on a "DCpower-supply line" 344 a (twice peak) potential level and on a "return"line 346 a potential level one half the line 344 potential level. Toimprove the power factor DC power supply 322 presents to an AC powerline (by restricting the amount of power the DC power supply can obtainfrom the AC power line during peaks of the line cycle), the DC powersupply is connected in series with power-factor-correcting network 320across a 120 volt, 60 Hz, AC power line, which is represented by a"neutral" line 348 and a "hot" line 350. Switches (transistors) 324 and326 are connected in a totem-pole configuration in which the channels ofthe transistors are connected in series between DC power-supply line 344and reference line 342. In other words, the channel of switch(transistor) 324 is configured with one end of the channel connected toline 344 and with the other end of the channel connected to a("high-frequency AC power-source") line 356., and, the channel of switch(transistor) 326 is configured with one end of the channel connected toline 356 and with the other end of the channel coupled (by a resistor,not shown) to line 342. The gates of switches (transistors) 324 and 326are each coupled by a respective one of two lines, designated 362 and364, to pulse generator 330. (In one embodiment) pulse generator 330 isconfigured to drive the switches (transistors), in turn, so as todevelop on line 356, a source of high-frequency AC power, the waveformof which approximates a square wave. Load (lamp) 312 is coupled bycurrent-limiting network 328 between high-frequency AC power-source line356 and return line 346. Specifically, current-limiting network 328 isconnected to high-frequency AC power-source line 356, return line 346,and a line 368., and, load (lamp) 312 is connected between line 368 and(in this embodiment) return line 346.

Unlike the network disclosed in the above-mentioned Ronald A. Lesea U.S.Pat. No. 4,415,839 embodiment, current-limiting network 328 includes acapacitor 90 an inductor 392, and another capacitor 394, all connectedin what is referred to herein as a "high-pass" "C-L-C" or "T-section"configuration (network). Specifically, capacitor 90 is connected betweenhigh-frequency AC power-source line 56 and a node 396; inductor 392 isconnected between node 396 and return line 346; and, capacitor 394 isconnected between node 396 and line 368. Current-limiting network 328 isoperative to provide an impedance transformation, providing a relativelyhigh impedance to load (lamp) 312 while providing a relatively lowimpedance at, or near, a zero degree phase angle, to switches(transistors) 324 and 326, reducing the level of the current through thetransistors. Further, current-limiting network 328 is useful in that itmay provide an increased starting potential across load (lamp) 312.

In addition, capacitors 390 and 394 provide "DC blocking." As aconsequence it is not necessary that DC power supply 322 provide a(half-level potential on) return line 346. Current-limiting network 328and load (lamp) 312 can be connected to, for example,reference-potential line 342.

Preferably, the components of current-limiting network 328 havecomponent values calculated in accordance with the following formulas:

    Rm((Eout/Ein).sup.2 * Rin * (Rin+Rl)-2 * Eout * Rin * Rl/Ein)/(((Eout/Ein).sup.2 * Rin)-Rl);

    Qin=((Rm/Rin)-1).sup.1/2 ;

    Qout=((Rm/Rl)-1).sup.1/2 ;

    Xc(390)=-Rin * ((Rm/Rin)-1).sup.1/2 ;

    Xc(394)=-Rl * ((Rm/Rl)-1).sup.1/2 ;

    Xl(392)=Rm/(((Rm/Rin)-1).sup.1/2 +((Rm/Rl)-1).sup.1/2);

    Eout=Ein * Xl(392)/(Xc(390)+Xl(392)); and,

    Xin=Xl(392)+Xc(390).

where:

Ein is the RMS output voltage level which is developed by thehigh-frequency AC power-source (between lines 356 and 346). Thehigh-frequency AC power-source disclosed in the above-mentioned RonaldA. Lesea U.S. Pat. No. 4,415,839 develops a worst case RMS outputvoltage level of approximately 100 volts. (When connected to a 120 volt,60 Hz power line, power-factor-correcting network 320 restricts thelevel of the (twice peak) potential level developed on line 344 to apotential level of approximately 280 volts. Allowing for low lineconditions and Fourier losses, yields a line 356 RMS output voltagelevel of approximately 100 volts.)

Eout is the desired RMS open-circuit output voltage level which is to bedeveloped across load (lamp(s)) 312 (between lines 368 and 346) beforethe lamp(s) ignite.

Rl is the loaded lamp impedance obtained by dividing the numberrepresenting the level of the voltage developed across the lamp(s) atthe desired operating current by the number representing the lampoperating current. The series combination of two F40T12 lamps operatingat a current level of 0.3 amperes has a loaded lamp impedance ofapproximately 700 ohms. (The lower lamp current is used because of theimproved lamp efficacy at high frequencies.)

Rin is the input impedance which is to be presented by current-limitingnetwork 328 to the high-frequency AC power-source (between lines 356 and346) to yield the desired lamp power level. In other words, Rin is equalto the square of the value representing Ein divided by the valuerepresenting the desired lamp power. For a high-frequency ACpower-source (which appears to the current-limiting network as a"voltage source") delivering an RMS output voltage level of 130 voltsand for a lamp power of 65 watts, an input impedance of 250 ohms isused.

Rm is a dependent variable, a unique solution for which is defined bythe above equations given Ein, Eout, Rl, and Rin.

Qin is the resultant loaded L-section input Q presented bycurrent-limiting network 328 to the high-frequency AC power-source(between lines 356 and 346). It should be noted that for the embodimentof current-limiting network (328) shown in FIG. 3, no independentcontrol of the input Q is available.

Qout is the resultant loaded L-section output Q presented bycurrent-limiting network 328 to load (lamp(s)) 312 (between lines 368and 346).

Xc(390) is the resultant capacitive reactance of capacitor 390.

Xc(394) is the resultant capacitive reactance of capacitor 394.

Xl(392) is the resultant inductive reactance of inductor 392.

Xin is the resultant open circuit (no load) reactance looking intocurrent-limiting network 328 (before lamp(s) 312 ignite). It isimportant to note that this is non-zero. In other words, a resonantcondition does not exist. Of course, were a resonant condition to exist,an infinite current would result and damage to the components (capacitor390 and transistors 324 and 326) would result.

Preferably, for driving (as a load 312) the series connection of twoF40T12 lamps from a 120 volt AC power line, the following componentvalues are employed:

Given:

Ein=100 volts;

Eout=450 volts;

Rl=700 ohms; and

Rin=250 ohms;

Then:

Ein=100.0 volts;

Eout=450.0 volts;

Qin=1.402004.,

Qout=0.2432048;

Rin=250.0 ohms;

Rl=700.0 ohms;

Rm=741.4040;

Xc(390)=-350.5011 ohms.,

Xc(394)=-170.2434 ohms;

Xl(392)=450.6442 ohms; and,

Xin=100.1432 ohms.

Preferably, inductor 392 is wound on a core of the type which isdesignated PQ by TDK and which is of the material which is designatedH7C1.

The presently preferred embodiment of a gaseous-discharge-lightingsystem in accordance with the present invention is illustrated in FIG. 4of the drawing generally designated by the number 400.Gaseous-discharge-lighting system 400 employs a source of high-frequencyAC power 402; a current-limiting network 404; and a (load that employsat least one) gaseous discharge lamp 406. Current-limiting network 404includes a capacitor 410, a transformer 412, and another capacitor 414,all connected in what is referred to herein as a "high-pass" "C-L-X-C"or "T-section" configuration (network). Specifically, capacitor 410 isconnected between a high-frequency AC power-source hot line 420, whichis connected to high-frequency AC power source 402, and a line 422.Transformer 412 is configured with the primary winding of thetransformer connected between line 422 and a high-frequency ACpower-source return line 424, which is also connected to high-frequencyAC power source 402, and with the secondary winding of the transformerconnected between a pair of lines, which are respectively designated 426and 428. Capacitor 414 is connected between line 426 and a line 430.Finally, load (lamp) 406 is connected between lines 430 and 428.

In one embodiment, transformer 412 has a primary winding reactance whichis the same as the reactance of inductor 392 of current-limiting network328 (shown in FIG. 3), and has a turns ratio of 1:1. As a consequence,transformer 412 functions as the combination of an inductor (392) and an"ideal" transformer. Thus, current-limiting network 406 is,functionally, quite similar to current-limiting network 328. Likecurrent-limiting network 328, current-limiting network 404 is, also,operative to provide an impedance transformation, providing a relativelyhigh impedance to lamp 406 while providing a relatively low impedanceat, or near, a zero degree phase angle, to high-frequency AC powersource 402, reducing the level of the current through the transistors.Further, current-limiting network 404 is useful in that it may providean increased

starting potential across lamp 406. However, unlike current-limitingnetwork 328, current-limiting network 404 is, in addition, operative toprovide greater isolation (safety) and an extra degree of designfreedom.

Preferably, the components of current-limiting network 404 havecomponent values calculated in accordance with the following formulas:

    Nsp=(Rl/Rpri).sup.1/2 ;

    Epri=Eout/Ein/Nsp;

    Rm=(Epri.sup.2 * Rin * (Rin+Rpri)-2 * Epri * Rin * Rpri)/((Epri.sup.2 * Rin)-Rpri);

    Rpri>Rin;

    Qin=((Rm/Rin)-1).sup.1/2 ;

    Qout=((Rm/Rpri)-1).sup.1/2 ;

    Xc(410)=-Qin * Rin;

    Xlp(412)=Rm/Qin+Qout);

    Xc(414)=-Qout * Rl;

    Xin=Xlp(412)+Xc(410); and,

    Eoact=Ein * Xlp(412) * Nsp/Xin.

Where:

Ein is the RMS output voltage level which is developed by high-frequencyAC power-source 400 (between lines 420 and 424).

Eout is the desired RMS open-circuit output voltage level which is to bedeveloped across load (lamp(s)) 406 (between lines 430 and 428) beforethe lamp(s) ignite.

Rl is the loaded lamp impedance.

Rin is the input impedance which is to be presented by current-limitingnetwork 404 to high-frequency AC power-source 400 (between lines 420 and424) to yield the desired lamp power level.

Rm is a dependent variable, a unique solution for which is defined bythe above equations given Ein, Eout, Rl, Rin, and Rpri.

Qin is the resultant loaded L-section input Q presented bycurrent-limiting network 404 to high-frequency AC power-source 400(between lines 420 and 424). It should be noted that for the embodimentof current-limiting network (404) shown in FIG. 4, independent controlof the input Q is now available.

Qout is the resultant loaded L-section output Q presented bycurrent-limiting network 404 to lamp(s) 406 (between lines 430 and 428).

Xc(410) is the resultant capacitive reactance of capacitor 410.

Xc(414) is the resultant capacitive reactance of capacitor 414.

Xlp(412) is the resultant inductive reactance of the primary oftransformer 412.

Xin is the resultant open circuit (no load) reactance looking intocurrent-limiting network 404 (before lamp(s) 406 ignite). It isimportant to note that this is non-zero. In other words, a resonantcondition does not exist. Of course, were a resonant condition to exist,an infinite current would result, the core of transformer 412 wouldsaturate and damage to the components would result.

Nsp is the turns ratio (secondary-to-primary) of transformer 412.

Rpri is the impedance at the transformer primary. Rpri is a newindependent variable, employed to establish Qin. Rpri must be greaterthan Rin.

Epri is a voltage ratio.

Eoact is the actual RMS open-circuit output voltage level which is to bedeveloped across load (lamp(s)) 406 (between lines 430 and 428) beforethe lamp(s) ignite. Eoact, when checked against Eout, provides a meansof ascertaining when certain boundary conditions have been exceeded.

Preferably, for driving (as a load 312) the series connection of twoF40T12 lamps from a 120 volt AC power line, the following componentvalues are employed:

Given:

Ein=100 volts;

Eout=450 volts;

Rl=700 ohms;

Rin=250 ohms; and

Rpri=1000;

Then:

Ein=100.0 volts;

Eoact=450.0 volts;

Eout=450.0 volts;

Epri=5.378529;

Nsp=0.836660;

Qin=1.753919;

Qout=0.138050;

Rin=250.0 ohms;

Rl=700.0 ohms;

Rm=1019.1 ohms;

Rpri=1000.0 ohms;

Xc(410)=-438.4797 ohms;

Xc(414)=-96.63516 ohms.,

Xin=108.1432 ohms; and,

Xlp(412)=538.6623 ohms.

Preferably, transformer 412 is wound on a core of the type which isdesignated PQ by TDK and which is of the material which is designatedH7CI. Wound on the core is 112 turns of heavy Nylon-Polyester insulated27 gauge wire for the transformer primary and 100 turns of heavyNylon-Polyester insulated 30 gauge wire for the transformer secondary.

Unfortunately, mathematical "boundary conditions" impose certainlimitations on the range of component values (generally, and on themaximum lamp impedance in particular) which may be "realized." Toprovide "realizable" solutions in these cases, a small inductor issubstituted for capacitor 414 (shown in FIG. 4). More specifically, thisembodiment of a gaseous-discharge-lighting system in accordance with thepresent invention is illustrated in FIG. 5 of the drawing generallydesignated by the number 500. Gaseous-discharge-lighting system 500employs a source of high-frequency AC power 502; a current-limitingnetwork 504., and a (load that employs at least one) gaseous dischargelamp 506. Current-limiting network 504 includes a capacitor 510 atransformer 12, and a inductor 514, all connected in what is referred toherein as a "high-pass" "C-L-X-L" configuration (network). Specifically,capacitor 510 is connected between a high-frequency AC power-source hotline 520, which is connected to high-frequency AC power source 502, anda line 522. Transformer 512 is configured with the primary winding ofthe transformer connected between line 522 and a high-frequency ACpower-source return line 524, which is also connected to high-frequencyAC power source 502, and with the secondary winding of the transformerconnected between a pair of lines, which are respectively designated 526and 528. Inductor 514 is connected between line 526 and a line 530.Finally, load (lamp) 506 is connected between lines 530 and 528.

Like current-limiting network 404, current-limiting network 504 isoperative to provide an impedance transformation, providing a relativelyhigh impedance to lamp 506 while providing a relatively low impedanceat, or near, a zero degree phase angle, to high-frequency AC powersource 502, reducing the level of the current flowing through thetransistors. Further, like current-limiting network 404,current-limiting network 504 is useful in that it may provide anincreased starting potential across lamp 506. In addition, likecurrent-limiting network 404, current-limiting network 504 is operativeto provide greater isolation (safety) and an extra degree of designfreedom.

Preferably, the components of current-limiting network 504 havecomponent values calculated in accordance with the following formulas:

    Nsp=(Rl/Rpri).sup.1/2 ;

    Epri=Eout/Ein/Nsp;

    Rm=(Epri.sup.2 * Rin * (Rin+Rpri)-2 * Epri * Rin * Rpri)/((Epri.sup.2 * Rin)-Rpri);

    Rpri>Rin;

    Qin ((Rm/Rin)-1).sup.1/2 ;

    Qout ((Rm/Rpri)-1).sup.1/2 ;

    Xc(510) Qin * Rin;

    Xlp(512)=Rm/(Qin+Qout);

    Xl(514) Qout * Rl;

    Xin Xlp(512)+Xc(510); and,

    Eoact=Ein * Xlp(512) * Nsp/Xin.

Where:

Ein is the RMS output voltage level which is developed by high-frequencyAC power-source 500 (between lines 520 and 524).

Eout is the desired RMS open-circuit output voltage level which is to bedeveloped across load (lamp(s)) 506 (between lines 530 and 528) beforethe lamp(s) ignite.

Rl is the loaded lamp impedance.

Rin is the input impedance which is to be presented by current-limitingnetwork 504 to high-frequency AC power-source 500 (between lines 520 and524) to yield the desired lamp power level.

Rm is a dependent variable, a unique solution for which is defined bythe above equations given Ein, Eout, Rl, Rin, and Rpri.

Qin is the resultant loaded L-section input Q presented bycurrent-limiting network 504 to high-frequency AC power-source 500(between lines 520 and 524). It should be noted that for the embodimentof current-limiting network (504) shown in FIG. 5, independent controlof the input Q is now available.

Qout is the resultant loaded L-section output Q presented bycurrent-limiting network 504 to lamp(s) 506 (between lines 530 and 528).

Xc(510) is the resultant capacitive reactance of capacitor 510.

Xl(514) is the resultant inductive reactance of inductor 514.

Xlp(512) is the resultant inductive reactance of the primary oftransformer 512.

Xin is the resultant open circuit (no load) reactance looking intocurrent-limiting network 504 (before lamp(s) 506 ignite). It isimportant to note that this is non-zero. In other words, a resonantcondition does not exist. Of course, were a resonant condition to exist,an infinite current would result, the core of transformer 512 wouldsaturate and damage to the components would result.

Nsp is the turns ratio (secondary-to-primary) of transformer 512.

Rpri is the transformer impedance. Rpri is a new independent variable,employed to establish Qin. Rpri must be greater than Rin.

Epri is a voltage ratio.

Eoact is the actual RMS open-circuit output voltage level which is to bedeveloped across load (lamp(s)) 506 (between lines 530 and 528) beforethe lamp(s) ignite. Eoact, when checked against Eout, provides a meansof ascertaining when certain boundary conditions have been exceeded.

Preferably, for driving (as a load 506) the series connection of twoF40T12 lamps from a 120 volt AC power line, the following componentvalues are employed:

Given:

Ein=100 volts;

Eout=450 volts;

Rl=700 ohms;

Rin=250 ohms; and

Rpri=2800;

Then:

Ein=100.0 volts;

Eoact=450.0 volts;

Eout=450.0 volts;

Epri=9000;

Nsp=0.500000;

Qin=3.204581;

Qout=0.078684;

Rin=250.0 ohms;

Rl=700.0 ohms;

Rm=2817.3 ohms;

Rpri=2800.0 ohms;

Xc(510)=-801.15 ohms;

Xl(514)=55.08 ohms;

Xin=100.1432 ohms., and,

Xlp(512)=901.2885 ohms.

Preferably, transformer 512 is wound on a core of the type which isdesignated PQ by TDK and which is of the material which is designatedH7CI. Wound on the core is 173 turns of heavy Nylon-Polyester insulated28 gauge wire for the transformer primary and 100 turns of heavyNylon-Polyester insulated 30 gauge wire for the transformer secondary.

Of course, for maximum efficiency, it is important that the loaded Q ofthe above-mentioned current-limiting networks be as low as possible(since the efficiency of such a network is equal to the quantity oneminus the loaded (running) Q of the network (the sum of all of theindividual (component) Qs of the network) all divided by the unloaded Qof the network (the sum of all of the individual (component) Qs of thenetwork.) However, when driven by a high-frequency AC power-sourcehaving a square-type waveform, such networks may couple to the lamp(s)certain "spikes" (square-wave edges). Such spikes may exceed the "crestfactor" (peak to RMS potential level) limitations of the of the lamp(s)or cause certain undesirable interactions of the negative resistance ofthe lamp(s) and the network. Thus, in certain embodiments of lightingsystems in accordance with the present invention, "Q enhancing" elementsare included in the associated current-limiting networks.

Specifically, in FIG. 6A, "an input Q-enhanced" current-limiting networkis illustrated generally designated 600. Current-limiting network 600includes a "Q-enhancing" inductor 602, a capacitor 604, a transformer606, and another capacitor 608. The primary of transformer 606 isconnected in series with inductor 602 and capacitor 604 between a pairof current-limiting network 600 input lines 610 and 612; and, thesecondary of the transformer is connected in series with capacitor 608between a pair of current-limiting network 600 output lines 616 and 618.

In FIG. 6B, "a transformer primary Q-enhanced" current-limiting networkis illustrated generally designated 620. Current-limiting network 620includes a capacitor 622, a "Q-enhancing" capacitor 624, a transformer626, and another capacitor 628. The primary of transformer 626 isconnected in series with capacitor 622 between a pair ofcurrent-limiting network 620 input lines 630 and 632; and, the secondaryof the transformer is connected in series with capacitor 628 between apair of current-limiting network 620 output lines 636 and 638. Capacitor624 is connected in parallel with the primary winding of transformer626.

"A transformer secondary Q-enhanced" current-limiting network isillustrated in FIG. 6C, generally designated 640. Current-limitingnetwork 640 includes a capacitor 642, a transformer 644, a "Q-enhancing"capacitor 646, and another capacitor 648. The primary of transformer 644is connected in series with capacitor 642 between a pair ofcurrent-limiting network 640 input lines 650 and 652; and, the secondaryof the transformer is connected in series with capacitor 648 between apair of current-limiting network 640 output lines 656 and 658. Capacitor644 is connected in parallel with the secondary winding of transformer646.

Finally, in FIG. 6D, "an output Q-enhanced" current-limiting network isillustrated generally designated 660. Current-limiting network 660includes a capacitor 662, a transformer 664, another capacitor 666 and a"Q-enhancing" inductor 668. The primary of transformer 664 is connectedin series with capacitor 662 between a pair of current-limiting network660 input lines 670 and 672; and, the secondary of the transformer isconnected in series with capacitor 666 and inductor 668 between a pairof current-limiting network 660 output lines 676 and 678.

In addition to their use for "Q-enhancement," the added inductor(inductor 602 for current-limiting network 600, illustrated in FIG. 6D,and inductor 668 for current-limiting network 660, illustrated in FIG.6D) are useful for current-level sampling. In other embodiments, a smallcurrent-sampling transformer is substituted for the extra inductor.

A disadvantage of many lighting systems in which multiple lamps areconnected in series is that when one lamp fails, all of the lamps "goout." Illustrated in FIG. 7 of the drawing generally designated by thenumber 700 is an embodiment of a current-limiting network in accordancewith the present invention configured to drive the parallel combinationof multiple gaseous discharge (fluorescent) lamps. Specifically,current-limiting network 700 is shown to include a capacitor 702, atransformer 704, and an inductor 706. The primary of transformer 704 isconnected in series with capacitor 702 between a pair ofcurrent-limiting network 700 input lines 710 and 712; and, the secondaryof the transformer is connected in series with inductor 706 between apair of lines 716 and 718. In addition, current-limiting network 700 isshown to include four, additional, capacitors, respectively designated720, 722, 724, and 726. Capacitor 720 is connected in series with a lamp730 between lines 716 and 718. Similarly, capacitor 722 is connected inseries with a lamp 732 between lines 716 and 718. A lamp 734 is coupledby capacitor 724 between lines 716 and 718; and, also connected betweenthe lines, is the series combination of capacitor 726 and a lamp 736.

In another embodiment, a capacitor is substituted for inductor 706 andinductors are substituted, one for each of capacitors 720, 722, 724, and726.

Also, to avoid the "one-out-all-out" problem, illustrated in FIG. 8 ofthe drawing generally designated by the number 800 is an embodiment of acurrent-limiting network in accordance with the present inventionconfigured to drive a "quasi-parallel" combination of multiple gaseousdischarge (fluorescent) lamps. Specifically, current-limiting network800 is shown to include an a capacitor 802, a transformer 804, anothercapacitor 806, and yet four additional capacitors, all connected in whatis referred to herein as a "high-pass" "C-L-X-PI" configuration(network). The primary of transformer 804 is connected in series withcapacitor 802 between a pair of current-limiting network 800 input lines810 and 812; and, the secondary of the transformer is connected inseries with capacitor 806 between a pair of lines 816 and 818. The fouradditional capacitors, which are respectively designated 820, 822, 824,and 826, are connected in series between lines 816 and 818. The fouradditional capacitors are each connected in parallel with acorresponding one of four lamps, which are respectively designated 830,832, 834, and 836. More specifically, capacitor 820 is connected inparallel with lamp 830 between line 816 and a line 840; capacitor 822 isconnected in parallel with lamp 832 between line 840 and a line 842;capacitor 824 is connected in parallel with lamp 834 between line 842and a line 844; and, capacitor 826 is connected in parallel with lamp836 between lines 844 and 818.

Preferably, the components of current-limiting network 800 havecomponent values calculated in accordance with the following formulas:

    Xc(total)=Xc(830)+Xc(832)+Xc(834)+Xc(836);

    Xls(804)=Rsec/Qout;

    Xc(806)=-((Rsec * Qout)+(Rsec * Rl/Xc(total))/Qout.sup.2 +1);

    Xc(total)=-Rl/((Rl * (Qout.sup.2 +1)/Rsec) -1).sup.1/2 ;

    Rpri Rsec/N.sup.2

    Xs(804)=Xls(804) * (Xc(806)+Xc(total)/Sls(804)+Xc(806)+Xc(total));

    Eout=Epri * N * Xc(total)/(Xc(806)+Xc(total));

    Qin ((Rpri/Rin)-1).sup.1/2 ;

    Xc(802)=-Rin * Qin;

    Xl(804)=Rpri/Qin;

    Epri=((Ein * Xl(804) * Xs(804)/N.sup.2)/(Xl(804)+Xs(804)/N.sup.2))/Xin;

    Xlp(804)=(Xl(804 * Xls(804)/N.sup.2)/(Xl(804)+Xls(804)/N.sup.2))

    Xin Xc(802)+((Xl(804) * Xs(804)/N.sup.2)/(Xl(804)+Xs(804)/N.sup.2))

Where:

Ein is the RMS output voltage level which is developed by thehigh-frequency AC power-source (between lines 810 and 812).

Eout is the desired RMS open-circuit output voltage level which is to bedeveloped across load (lamp(s)) 830, 832, 834, and 836 (between lines816 and 818) before the lamp(s) ignite.

Rl is the loaded lamp impedance.

Rin is the input impedance which is to be presented by current-limitingnetwork 800 to the high-frequency AC power-source (between lines 810 and812) to yield the desired lamp power level.

Qin is the resultant loaded L-section input Q presented bycurrent-limiting network 800 to the high-frequency AC power-source(between lines 816 and 818).

Qout is the resultant loaded PI-section output Q presented bycurrent-limiting network 800 to lamp(s) 830, 832, 834, and 836 (betweenlines 816 and 818).

Xc(802) is the resultant capacitive reactance of capacitor 802.

Xc(806) is the resultant capacitive reactance of capacitor 806.

Xc(820) is the resultant capacitive reactance of capacitor 820.

Xc(822) is the resultant capacitive reactance of capacitor 822.

Xc(824) is the resultant capacitive reactance of capacitor 824.

Xc(826) is the resultant capacitive reactance of capacitor 826.

Xls(804) is the required inductive reactance for the secondary oftransformer 804, neglecting the primary.

Xl(804) is the required inductive reactance for the primary oftransformer 804, neglecting the secondary.

Xlp(804) is the resultant inductive reactance for the primary oftransformer 804.

Xin is the resultant open circuit (no load) reactance looking intocurrent-limiting network 800 (before lamp(s) 830, 832, 834, and 836ignite). It is important to note that this is non-zero. In other words,a resonant condition does not exist. Of course, were a resonantcondition to exist, an infinite current would result, the core oftransformer 804 would saturate and damage to the components wouldresult.

N is the turns ratio (primary-to-secondary) of transformer 804.

Rpri is the transformer impedance. Rpri must be greater than Rin.

Epri is a voltage ratio.

Preferably, for driving the series connection of four F032T8 lamps froma 120 volt AC power line, the following component values are employed:

Given:

Ein=105 volts;

Eout=1400 volts;

Rl=2600 ohms;

Rin=130 ohms; and

Qout=2.5;

Then:

Eout=1400.0 volts.,

Epri=266.9231;

N=9.440920.,

Qin=0.549050;

Rin=130.0 ohms.,

Rl=2600.0 ohms;

Rpri=169.1892 ohms;

Rsec=15080.00 ohms;

Xc(802)=-71.37647 ohms.,

Xc(806)=-4160.000 ohms.,

Xc(total)=-5200.000 ohms;

Xin=46.28448 ohms;

Xl(804)=308.1492 ohms;

Xlp(804)=55.48917 ohms;

Xls(804)=6032.000 ohms; and

Xs(804)=16965.00 ohms.

Preferably, transformer 512 is wound on a core of the type which isdesignated PQ by TDK and which is of the material which is designatedH7C1.

In another embodiment, a inductor is substituted for capacitor 806. Inyet another embodiment, inductors are substituted, one for each ofcapacitors 820, 822, 824, and 826.

In a presently preferred embodiment, illustrated in FIG. 9, used is acombination of the lighting systems shown in FIGS. 7 and 8.

Although lighting systems in accordance with the present invention mayuse a simple square-wave-type high-frequency AC power source, the"Electronic Ballast For Gaseous Discharge Lamps" which is disclosed inthe above-mentioned Ronald A. Lesea U.S. Pat. No. 4,415,839 uses amodified square-wave-type source (having dead time between pulses), thefrequency and/or pulse width of which is varied so as to control thelevel of the power delivered to the load (lamps). Not only are thecurrent-limiting networks disclosed herein compatible with such ahigh-frequency AC power source, but the networks are suitable for usewith high-frequency AC power sources which develop other type waveformsincluding sinusoidal, rectangular, pulse, square, modified square withdead time, and triangular. Also, not only are the current-limitingnetworks disclosed herein compatible with high-frequency AC powersources (such as those disclosed in the above-mentioned Ronald A. LeseaU.S. Pat. No. 4,415,839) which appear to the network as voltage sources(high-frequency AC power sources which appear to their respectivenetwork as having a relatively low impedance, as illustrated in FIG.10A, designated 900), but they are compatible with high-frequency ACpower sources which appear to the network as current sources(high-frequency AC power sources which appear to their respectivenetwork as having a relatively high impedance, as illustrated in FIG.10B, designated 910). (Of course, when the current-limiting network isdriven by a high-frequency AC power sources which appear to the networkas a current source, Rin is equal to the value representing the desiredlamp power divided by the square of the value representing the level ofthe current delivered to the network by the source.)

It is contemplated that after having read the preceding disclosure,certain alterations and modifications of the present invention will nodoubt become apparent to those skilled in the art. It is thereforintended that the following claims be interpreted to cover all suchalterations and modifications as fall within the true spirit and scopeof the invention.

What is claimed is:
 1. A lighting system comprising in combination:ahigh-frequency AC power source (402); a load (406) including at last onegaseous discharge lamp; and a current-limiting network (404)including,first capacitor means (410), second capacitor means (414), andtransformer means (412) having primary winding means coupled in serieswith said first capacitor means across said high-frequency AC powersource and secondary winding means coupled in series with said secondcapacitor means across said load.
 2. A lighting system as recited inclaim 1 wherein said high-frequency AC power source appears to saidcurrent-limiting network as a voltage source.
 3. A lighting system asrecited in claim 1 wherein said high-frequency AC power source appearsto said current-limiting network as a current source.
 4. A lightingsystem as recited in claim 1 wherein said first capacitor means has afirst, predetermined, capacitive reactance and wherein said secondcapacitor means has a second, predetermined, capacitive reactance themagnitude of which is less than the magnitude of said first capacitivereactance.
 5. A lighting system as recited in claim 1 wherein said firstcapacitor means has a first, predetermined, capacitive reactance Xc(1),wherein said primary winding means has a, predetermined, inductivereactance Xlp(1), wherein said second capacitor means has a second,predetermined, capacitive reactance Xc(2), wherein said transformermeans has a transformer impedance Rpri, wherein Xc(1), Xlp(1), Xc(2),and Rpri conform to the relationship:

    Rm=((Eout/Ein/((Rl/Rpri).sup.1/2)).sup.2 * Rin * (Rin+Rpri)-2 * (Eout/Ein/((Rl/Rpri).sup.1/2)) * Rin * Rpri)/(((Eout/Ein/((Rl/Rpri).sup.1/2)).sup.2 * Rin)-Rpri);

    Xc(1)=-Rin * ((Rm/Rin)-1).sup.1/2 ;

    Xlp(1)=Rm/(((Rm/Rpri)-1).sup.1/2 +((Rm/Rin)-1).sup.1/2);

    Xc(2)=-Rl * ((Rm/Rpri)-1).sup.1/2 ;

Where: Rl is a predetermined loaded lamp impedance presented to saidcurrent-limiting network by said load; Rin is a predetermined inputimpedance presented by said current-limiting network to saidhigh-frequency AC power-source; Eout is a predetermined open-circuitoutput voltage level developed by said current-limiting network acrosssaid load; Ein is a predetermined voltage level developed by saidhigh-frequency AC power-source across Rin; and Rm is a dependentvariable, which is defined by Ein, Eout, Rl, Rin, and Rpri.